Biomedical containers, such as those used for blood and intravenous solutions, are currently made of glass or poly(vinyl chloride). Glass is being replaced because of its weight, bulkiness, and susceptibility to breakage. Replacements for poly(vinyl chloride) are being sought because containers of poly(vinyl chloride) are made from extruded film by a rather involved process. Pellets are extruded into film, which is cut to the required sizes and two pieces are sealed on the sides and at the ends to form a bag. The bag is also fitted with one or more tubing connections. A simpler method of forming containers or bags for biomedical applications would be highly desirable. Extrusion blow molding of film or bottles provides a significant reduction in the number of steps, and consequently, the cost of producing biomedical containers. Extrusion blown film would require sealing two edges instead of four. The use of extrusion blown bottles for containers would be even simpler than using extrusion blown film because a bottle having the desired shape and openings could be blown in one step. Poly(vinyl chloride) used in many biomedical applications, such as containers for blood and intraveneous solutions, cannot be blow molded because of its high plasticizer content.
In order to take advantage of extrusion blow molding, techniques, a polymer must have sufficient melt strength to be blow moldable into an object. The polymer must have the physical, tensile, and thermal properties necessary for specific end-use applications. A polymer is described as having melt strength when it can support its own weight in the molten state after being extruded from a die. When a polymer without melt strength is melt extruded downward from a die, the melt rapidly drops and forms a thin string or breaks. Such polymers are not useful for extrusion blow molding objects. When polymers have sufficient melt strength, they can be extruded downward in the shape of a hollow cylinder. Bottles can be blown by clamping a bottle mold around the molten hollow cylinder into which air is blown to form the bottle. This process is referred to herein as "extrusion blow molding."